1. Field of the Invention
This invention relates to synthetic polyphenol monomers and oligomers, derivatives thereof, and methods for making and using the same.
2. Related Background Art
Polyphenols are a highly diverse group of compounds (Ferreira, D., Steynberg, J. P., Roux, D. G. and Brandt, E. V., Tetrahedron, 48, (10), 1743-1803 (1992)) which widely occur in a variety of plants, some of which enter into the food chain. In many cases, they represent an important class of compounds present in the human diet. Although some of the polyphenols are considered to be non-nutritive, interest in these compounds has arisen because of their possible beneficial effects on health.
For instance, quercetin (a flavonoid) has been shown to possess anticarcinogenic activity in experimental animal studies (Deschner, E. E., Ruperto, J., Wong, G. and Newmark, H. L., Carcinogenesis, 7, 1193-1196 (1991) and Kato, R., Nakadate, T., Yamamoto, S. and Sugimura, T., Carcinogenesis, 4, 1301-1305 (1983)). (+)-Catechin and (xe2x88x92)-epicatechin (flavan-3-ols) have been shown to inhibit Leukemia virus reverse transcriptase activity (Chu S.-C., Hsieh, Y.-S. and Lim, J.-Y., J. of Natural Products, 55, (2), 179-183 (1992)). Nobotanin (an oligomeric hydrolyzable tannin) has also been shown to possess anti-tumor activity (Okuda T., Yoshida, T., and Hatano, T., Molecular Structures and Pharmacological Activities of Polyphenolsxe2x80x94Oligomeric Hydrolyzable Tannins and Othersxe2x80x94Presented at the XVIth International Conference of the Groupe Polyphenols, Lisbon, Portugal, Jul. 13-16, 1992). Statistical reports have also shown that stomach cancer mortality is significantly lower in the tea producing districts of Japan. Epigallocatechin gallate has been reported to be the pharmacologically active material in green tea that inhibits mouse skin tumors (Okuda et al., ibid.). Ellagic acid has also been shown to possess anticarcinogen activity in various animal tumor models (Boukharta M., Jalbert, G. and Castonguay, A., Efficacy of Ellagitannins and Ellagic Acid as Cancer Chemopreventive Agentsxe2x80x94Presented at the XVIth International Conference of the Groupe Polyphenols, Lisbon, Portugal, Jul. 13-16, 1992). Proanthocyanidin oligomers have been disclosed (JP 4-190774) by the Kikkoman Corporation for use as antimutagens. The use of phenolic compounds in foods and their modulation of tumor development in experimental animal models has been recently presented at the 202nd National Meeting of The American Chemical Society (Phenolic Compounds in Foods and Their Effects on Health I, Analysis, Occurrence and Chemistry, Ho, C.-T., Lee, C. Y., and Huang, M.-T editors, ACS Symposium Series 506, American Chemical Society, Washington, D.C. (1992); Phenolic Compounds in Foods and Their Effects on Health II. Antioxidants and Cancer Prevention, Huang, M.-T., Ho, C.-T., and Lee, C. Y. editors, ACS Symposium Series 507, American Chemical Society, Washington, D.C. (1992)).
Procyanidin polyphenols, and particularly higher oligomers thereof, have recently been found to possess a broad spectrum of biological activity Reference is made to U.S. patent application Ser. No. 08/709,406 filed Nov. 6, 1996, now U.S. Pat. No. 6,015,913 issued Jan. 18, 2000 and U.S. application Ser. No. 08/317,226 filed Oct. 3, 1994, now U.S. Pat. No. 5,554,645 issued Sep. 10, 1996, each of which is incorporated herein by reference. These patents disclose a variety of health benefits provided by procyanidin polyphenols as well as a means of increasing the concentration of these beneficial polyphenols in extracts, foods, pharmaceutical preparations and chocolate compositions. Reference is also made to parent U.S. application Ser. No. 08/948,226 filed Oct. 9, 1997, now U.S. Pat. No. 6,207,842 issued Mar. 27, 2001, which discloses methods of preparing polyphenol oligomers, and specifically procyanidin polyphenols, the disclosure of which is also incorporated herein by reference.
Isolation, separation, purification, and identification methods have been established for the recovery of a range of procyanidin oligomers for comparative in vitro and in vivo assessment of biological activities. For instance, anti-cancer activity is elicited by pentameric through decameric procyanidins, but not by monomers through tetrameric compounds. Currently, gram quantities of pure ( greater than 95%) pentamer are obtained by time-consuming methods which are not satisfactory for obtaining a sufficient quantity of the pentamer for large scale pharmacological and bioavailability studies. Even greater effort is required to obtain gram quantities of higher oligomers, hexamers through dodecamers, for similar studies since they are present in the natural product in much lower concentrations than the pentamer. Additionally, increasing oligomeric size increases structural complexity. Factors such as differences in the chirality of the monomeric units comprising the oligomer, different interflavan bonding sites, differences in the chirality of the interflavan bonding, dynamic rotational isomerization of the interflavan bonds, and the multiple points of bonding at nucleophilic centers pose efficiency constraints on current analytical methods of separation and purification for subsequent identification.
These collective factors point to a need for synthesis methods to permit the unambiguous proof of both structure and absolute configuration of higher oligomers, to provide large quantities of structurally defined oligomers for in vitro and in vivo assessment and to provide novel structural derivatives of the naturally occurring procyanidins to establish the structure-activity relationships of these materials. Accordingly, it would be advantageous to develop a versatile synthetic process capable of providing large quantities of any desired polyphenol oligomer.
This invention is directed to a process for preparing a polyphenol oligomer comprised of coupled polyphenol monomeric, or flavanoid, units. The process of this invention comprises:
(a) protecting each phenolic hydroxyl group of a polyphenol monomer with a protecting group to form a protected polyphenol monomer having the formula: 
c is an integer from 1 to 3;
d is an integer from 1 to 4;
e is an integer from 0 to 2;
f is an integer from 0 to 2;
R1 is H, OH or OR3;
R and R3 are independently protecting groups; and
R2 is halo;
(b) functionalizing the 4-position of the protected polyphenol monomer to form a functionalized, protected polyphenol monomer having the formula; 
xe2x80x83wherein
c is an integer from 1 to 3;
d is an integer from 1 to 4;
e is an integer from 0 to 2;
f is an integer from 0 to 2;
y is an integer from 2 to 6;
R1 is H, OH or OR3;
R4 is H or R5;
R, R3 and R5 are independently protecting groups; and
R2 is halo;
(c) coupling the protected polyphenol monomer with the functionalized protected polyphenol monomer to form a protected polyphenol dimer, where the polyphenol monomeric units are the same or different; and
(d) optionally repeating the functionalizing and coupling steps to form a polyphenol oligomer having n monomeric units where n is 3 to 18.
The process of this invention also provides for the preparation of novel derivatives of the polyphenol oligomer. Halogenation of the functionalized protected polyphenol monomer provides a halogenated functionalized polyphenol monomer having the formula: 
wherein, c is 1 to 3; d is 1 to 4; e is 1 or 2; f is 1 or 2; y is 2 to 6; Rxe2x80x2 is H, OH, or OR3; R4 is H or R5; R, R3 and R5 are independently protecting groups; and R2 is halo substituent which maybe the same or different. This halogenated functionalized monomer may be used for the production of a halogenated polyhphenol oligomer by coupling of this monomer with either a protected polyphenol monomer or with a protected polyphenol oligomer. Alternatively, halogentated polyphenol oligomers may be prepared by direct halogentation of the polyphenol oligomers.
Other novel derivatives may be prepared by esterifying or glycosylating the polyphenol oligomer to produce a derivatized polyphenol oligomer. Formation of the derivatized oligomers may be conducted either prior to or subsequent to removal of the protecting groups from the phenolic hydroxyl groups of the polyphenol oligomer. Accordingly, this invention is also directed to novel polyphenol monomers, novel polyphenol oligomers, and novel derivatized polyphenol monomers and oligomers.